<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>test</title>
    <style>
        #mask{
            background-color: #eee;
            position: fixed;
            top: 0px;
            left: 0px;
            display: flex;
            align-items: center;
            justify-content: center;
            color: rgb(179, 179, 179);
        }
    </style>
</head>
<body>
    <form action="/api/add">
        <label>a的值:</label><input name="a">
        <br>
        <label>b的值:</label><input name="b">
        <button>提交表单</button>
    </form>
</body>
</html>